The rate of crystallization of calcium oxylate in synthetic urine will be measured with radioactive oxylate. The influence of different fractions of normal and stone-formers urine on the rate will be studied to identify substances in normal urine, absent in stone-formers urine, that inhibit crystallization. The concentrations of certain critical substances in the synthetic urine: phosphate, citrate, and magnesium ions, will be varied to assess their importance in the strong inhibitory effect of synthetic urine on the crystallization of calcium oxylate. Influence of these solutions on agglomeration of calcium oxylate crystals and on the hydrate structural type (tri-, di-, or mono-) of the calcium oxylate crystals will be followed with optical and electron microscopy and x-ray diffraction.